Reaction injection molding (RIM) has become an important process for the production of external automotive body parts and other types of molded products. The RIM process involves the intimate mixing of a polyisocyanate component and an isocyanate-reactive component followed by the injection of this mixture into a mold for subsequent rapid curing. The polyisocyanate component is typically based on a liquid polyisocyanate. The isocyanate-reactive component contains a high molecular weight isocyanate-reactive component, typically a polyol and/or amine polyether, and usually contains a chain extender containing amino and/or hydroxyl groups. U.S. Pat. No. 4,218,543 describes a RIM process currently being commercially used on a large scale.
While products produced by the RIM process have excellent physical properties, the use of the RIM process was previously limited by the necessity of using sprayed external mold release agents (e.g., waxes, soaps, and the like). These agents had to be sprayed onto the mold surface before each shot or every several shots. Recently, internal mold release agents have become available which obviate the need for external release agents. Specifically internal mold release agents containing zinc carboxylates where the carboxylate group contains from 8 to 24 carbon atoms has met with widespread commercial use. Release agents of this type are described in U.S. Pat. Nos. 4,519,965, 4,581,386 and 4,585,803; and British Patent No. 2,101,140. In using such zinc carboxylates it is necessary to mix the carboxylate with a compatibilizer which will solubilize the zinc carboxylate so that when the resultant mixture is mixed with the isocyanate-reactive components, the zinc carboxylate will possess improved resistance to precipitation. British Patent No. 2,101,140 describes the mixture of a zinc stearate and an epoxidized vegetable oil (such as epoxidized soybean oil).
U.S. Pat. Nos. 4,519,965 and 4,581,386 describe the use of compatibilizer selected from the group consisting of nitrogen-containing, isocyanate-reactive acyclic compounds and nitrogen-containing, isocyanate-reactive polymers. Preferred compatibilizers include polyether polyamines and amine- or hydroxy-terminated, amine-initiated polyethers. U.S. Pat. No. 4,585,803 describes the use of compatibilizers which are tertiary amine compounds which contain at least one tertiary nitrogen. The tertiary amine compounds described advantageously contain one or more hydroxy groups.
Although the combination of the zinc carboxylates and the compatibilizers noted have met with substantial commercial success, the search continues for other satisfactory compatibilizers.